Springed fan track liner

ABSTRACT

A containment system for a gas turbine engine includes a replaceable spring biased fan track assembly for use with a containment case. The fan track assembly includes a body of collapsible material that is positioned within a cavity of the fan case and a spring arrangement provides as system that is operable to perform during normal operating conditions as well as during catastrophic blade failure conditions. In particular, the improved fan track design contemplates a liner that displaces sufficiently at energies less than large foreign object destruction type events.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/772,396, filed Mar. 4, 2013, the contents of which are hereby incorporated in their entirety.

FIELD OF TECHNOLOGY

An improved liner for a fan case for a gas turbine engine, and more particularly, an improved fan track liner and method of mounting the liner to the fan case of a gas turbine engine.

BACKGROUND

Gas turbine engines are used extensively in high performance aircraft and they employ large fans that are positioned at the front of the engine so as to provide greater thrust and to reduce specific fuel consumption. This in turn, provides greater efficiencies and economical performance which is desired in the competitive airline industry. A fan is disposed within a duct and is driven by a shaft that is connected to the turbine and directs air rearwardly through the duct in the form of bypass air. The duct includes a fan casing that circumscribes the fan and the casing is capable of containing debris and minimizing damage to the engine in the event a catastrophic event occurs such as when birds, hailstones, or other debris enter the duct.

Fan casings can also be equipped with specialized blade containment structures that serve to minimize structural damage to the immediate surroundings of the engine in the event a fan blade is released from its hub during engine operation. This is known as a “blade-off” event, which can be catastrophic to an aircraft. Various configurations have been used for such containment structures including various methods of securing the containment structure to a fan casing.

One problem with utilizing traditional containment structures is that they fail to provide a sufficient containment of debris during a blade-off or other catastrophic event. This may be due to the containment structure being too rigid and not demonstrating the proper collapsible deformation characteristics that may be present during predetermined conditions. For example, it would not be desirable to have a fan track liner collapse due to ice impact. By contrast, having a liner that collapses during a blade-off, or other events, so as to minimize damage to the engine and its surroundings, could be helpful to the industry. It may also be helpful to provide a containment structure that has a predetermined collapsing and yielding characteristic or profile.

Traditional fan track liner designs require the released energy of a full fan blade to initiate the failure of the fan track liner so that the released material can be captured in the fan case hook. The liner typically has not been designed to fail under partial fan blade release because the energy associated with partial fan blade material can be equal to, or less than, the impact energy of normal ingested FOD (foreign object damage) such as ice or debris. Designing the fan track liner to fail under those conditions would require an unacceptably frequent replacement of the fan track liners, resulting in very high service costs. Designing a fan track liner that it is capable of tolerating FOD impact but that is also capable of yielding to release partial fan blade material to allow its capture outside the flow path remains an engineering challenge that has yet to be resolved.

Accordingly, a more reliable and robust solution for a fan track liner design is proposed. Such design is intended to satisfy at least two criteria of the fan track liner that have not been robustly satisfied by any designs to date. The improved deign is intended to be capable of tolerating impact from external environmental features such as ice or debris of a certain energy while also be capable of yielding to released fan blade material of lesser impact energy so that it may be captured by the fan case hook feature. Additionally, an improved design is proposed to exploit the advantages of a cassette-style panel that is bolted to the fan case.

The exemplary embodiment allows the fan track liner segments to be easily replaced in service, without risk of damaging the fan case, and resulting in less “aircraft on ground” time which directly translates into less money lost by the airline. The present concept further prevents the need for a repair allowance (extra thickness) to be designed into the fan case to allow for dressing out damage caused by the removal of the bonded-in fan track liner segments, which reduces fan case weight.

Various exemplary embodiments may overcome these problems and provide a containment structure that more fully meets the demands of today's aircraft industry.

BRIEF DESCRIPTION OF THE DRAWINGS

While the claims are not limited to a specific illustration, an appreciation of the various aspects is best gained through a discussion of various examples thereof. Referring now to the drawings, exemplary illustrations are shown in detail. Although the drawings represent the illustrations, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an example. Further, the exemplary illustrations described herein are not intended to be exhaustive or otherwise limiting or restricted to the precise form and configuration shown in the drawings and disclosed in the following detailed description. Exemplary illustrations are described in detail by referring to the drawings as follows:

FIG. 1 illustrates a schematic view of a gas turbine engine employing the improvements discussed herein;

FIG. 2 illustrates an exemplary embodiment of a springed fan track liner;

FIG. 3 illustrates an alternative exemplary embodiment using a hook-shaped spring member; and

FIG. 4 illustrates a graph showing the energies of various elements as a function of the deflection of the fan track liner of the present embodiments.

DETAILED DESCRIPTION

An improved fan track assembly provides an ability to tolerate ice impact (yet yield to fan blade material impact of lesser energy) is accomplished through an arrangement of a spring element interface between the fan track liner panel and the fan case at the front of the panel near the fan case hook, and a flexible joint at the aft end of the panel near the rear acoustic panel.

Exemplary illustrations of a gas turbine engine having a containment structure such as fan track liner assembly are described herein and are shown in the attached drawings. Exemplary fan track liner assemblies may include a one-piece removal tray that is positioned within a cavity of the fan case. The tray may be secured at a forward edge of the fan case cavity by either resting on, or being fastened to a fan case hook. The aft position of the tray may be positioned in place and held securely by a fastener.

The improved concept utilizes a spring biased fan track liner assembly that works in conjunction with a fan case that utilizes a hook feature positioned forward of the fan blade track so as to maintain the axial retention of released fan blade material. The concept affords enhanced fan track liner behavior during impact events of different natures and energy levels. There exists a range of impact energies for which the springed fan track liner assembly could both survive for continued operation and displacement during various conditions.

Turning now to the drawings, FIG. 1 illustrates a gas turbine machine 10 for use in connection with a high performance aircraft. The machine 10 includes a fan 12, a low pressure compressor and a high pressure compressor, 14 and 16, a combustor 18, and high pressure turbine and low pressure turbine, 20 and 22, respectively. The high pressure compressor 16 is connected to a first rotor shaft 24 and the low pressure compressor 14 is connected to a second rotor shaft 26. The shafts extend axially and are parallel to a longitudinal center line axis 28.

Ambient air 30 enters the fan 12 and is directed across a fan rotor 32 and into an annular duct 34 which in part is circumscribed by fan case 36. The bypass airflow 38 provides engine thrust while the primary gas stream 40 is directed to the combustor 18 and the high pressure turbine 20. The fan case 36 includes an improved fan track liner assembly 42, which can enhance containment of debris during predetermined events.

With reference to FIG. 2, a fan track liner assembly 42 is positioned within the fan track cavity 44. The fan track cavity 44 is a radially extending recess that is encompassed by a fan case inner surface 46, an aft located radially extended wall 48, a forwardly positioned accurate shaped wall 50, and an opening 52 that extends between the radially extending wall 48 and the wall 50. The cavity 44 has a depth similar to the length of the radially extending wall 48 and the cavity 44 is partially consumed by the volume defined by the external configuration of the fan track liner assembly 42. A void 54 is provided near a fan case hook 56, which provides a space for fragments of the blade 32, or other debris, to enter during a catastrophic event. The void 54 further provides a space for the fan track liner assembly 42 to be collapsed partially into during a catastrophic event.

The fan track liner assembly 42 may further include at least one biasing member such as, but not limited to, a leaf spring 58 positioned in the forward position of the assembly 42. The spring 58 provides a biasing force that impinges upon the fan case inner surface 46. One or more fasteners 60 may be used to secure the spring 58 to a top surface 62 of the assembly 42. It will be appreciated that other biasing members having other geometric configurations are contemplated with this assembly 42 and such a spring 58 may be positioned in locations other than that which is depicted herein.

The fan track liner assembly 42 can be mounted at its rearward location 76 by a fastener 64 and at its forward position 66 by a lip 68. The geometry of the lip 68 provides a radial interference between the fan track liner 76 and the fan case 36, preventing it from moving into the flow path 30. An advantage of this characteristic is that it facilitates the collapse of the fan track assembly 42 during a fan blade off event. There is no reliance on the uncontrollable failure of a bolt attachment, for example. Also, it does not, in any way, compromise the integrity of the fan case hook 56, whereas a bolting arrangement would require holes drilling through the hook that may induce some amount of weakness at that location.

The fan track liner assembly 42 is operable to yield next to the fan case hook 56 during a catastrophic event. The components of the fan track liner assembly 42 include an outer surface 72, a honeycomb core 74, and a liner 76 which lies adjacent the fan case inner surface 46. The liner 76 includes a first raised portion 78 and a second raised portion 80 that may collectively form one contiguous unitary piece of core 74. It will be appreciated that the core 74 could be comprised of portions having separate core members as well. The liner 76 outlines the top surface 62 of the first raised portion 78 and the second raised portion 80. The raised portion 78 impinges upon the fan case inner surface 46 and aids in holding the assembly 42 in place.

A void 82 provides a space in which core 74 does not exist so as to make the fan track liner assembly 42 lighter. The voids 54 and 82 further provide spaces or vacancies, which in turn, during a catastrophic event, allow the core 74 to be collapsed into the voids 54 and 82. It will be appreciated that the voids 54 and 82 may provide other features and benefits as well. Spring 58 may be compressed during an event, such a blade off situation, which in turn may permit debris to enter into voids 54 and 82 so as to provide a space to capture and retain such debris.

The spring 58 provides a sufficient biasing force so as to cause lip 68 of the liner 76 to engage the hook 56 of the fan case 36. By proving such a biasing force, the outer surface 72 of the assembly 42 remains substantially in alignment with the surface 84 of the hook 56. Such alignment provides improved laminar airflow 30 near the blade 32. The arrangement may be capable of tolerating debris of even greater energy than a current state-of-the-art design due to the absorption quality associated with the spring system. The “give” in the assembly 42 may reduce damage caused by impacting debris and thereby decrease service burden. The spring constant of the spring 58 is designed such that the core 74 is nominally positioned (fully pushed out, with the panel lip resting on the fan case hook 56, and with the surface of the abradable material 72 directly in-line with the flow path) under normal running conditions, so that there is no deficit to performance. However, it is designed to compress under any energy load beyond the normal pressure load of the flow path, which would be caused by normal operating FOD such as ice or external debris as well as abnormal debris such as fan blade material.

The construct of the assembly 42 may include a group of layered panels that extend at least the length of the fan blade airfoil axially and wrap all the way around the fan case 36 circumferentially. The inner most layer of the assembly 42 could be NOMEX® brand honeycomb filled with epoxy having a low density filler which serves as the abradable material or outer surface 72. The core 74 is the main body which may be constructed of aluminum honeycomb which adds stiffness to the assembly 42 and can be constructed of varying densities. Septum sheets may be used to separate the honeycomb core from the Nomex outer surface. The liner 76 acts as a backing tray and separates the core 74 of the panel from the fan case 36.

It will be appreciated that the core 74 may be made of other materials, and provide various collapsing characteristics, as is desired by the industry. The liner 76 performs a tray-like function, thus allowing the fan track liner assembly 42 to set within the fan track cavity 44, relatively easily during repair conditions. In this instance, no adhesive is used to secure the assembly 42 to the fan case 36, thus enhancing serviceability. The liner 76 can be made of a composite material, but it will be appreciated that it could be made of other materials. The liner 76 is depicted in a stepped configuration by virtue of portions 78 and 80. It will be appreciated that other geometric configurations are contemplated.

To install the fan track liner assembly 42, the forward section 60 of the fan track liner assembly 42 is inserted such that a lip 68 is inserted radially outward of the fan case hook 56, while the aft section 76 is rotated outward and bolted via fastener 64 to support member 86. The lip 68 rests upon the fan case hook 56 and it is not rigidly secured thereto. Thus, the lip 68 is operable to be displaced in the direction of arrow 88 during a catastrophic event. During such period, the lip 68 moves into the void 54 and provides a space for debris to accumulate. The fan blade 32 is shown with its tip 90 not in contact with the outer surface 72. Such condition could occur when the gas turbine 10 is not under load during normal operating conditions.

The fan track liner assembly 42 has a predetermined level of deflectability so as to allow it to perform under such conditions. An aerodynamic flow path 30 is directed to a leading edge 92 of the blade 32, which in turn generates a fan blade airflow 94, which in turn becomes bypass airflow 38 (FIG. 1). During a blade-off catastrophic event, blade debris could move forward, thus causing lip 68 to move in the direction of arrow 88. Under this condition, blade debris could be captured in the voids 54 and 82, and or the core 74 could deform and move into the voids. The fan hook 56 and voids aid in capturing debris during catastrophic events.

An aft section 76 of the fan track liner assembly 42 is shown rigidly secured by the fastener 64, which extends through a lip 86 that is a component of the liner 76. It will be appreciated that other fastening type devices 64 may be employed, utilizing other mechanical configurations. When the fan track liner assembly 42 is spring loaded within the fan track cavity 44, the assembly 42 is slightly compressed in the forward and radial directions, thus making it pre-loaded as the installer secures fastener 64 in place. By the fan track liner assembly 42 being slightly preloaded, pressure is maintained on lip 68 at or near the fan case hook 56. The nose 60 of the fan track liner 42 similarly is wedged against the fan case inner surface 46, which in turn causes the assembly 42 to be firmly secured in the cavity 44.

During operation, the forward position 66 is naturally biased in the direction opposing arrow 88. A continuous or sufficiently frequent contact with the fan case inner surface 46 is exhibited throughout its axial and circumferential spans to promote damping of the fan track liner assembly 42 through the use of one or more springs 58. This helps to prevent the excitation that extended sections of unsupported fan track liners may exhibit.

The lip 68 works as a catch or a stop so as to limit the assembly 42 from traversing into the flow path 30. However, during an event, such as a blade off event, the biasing force of spring 58 may be overcome by the force acting in the direction of arrow 88. During this condition, the spring 58 is compressed thus allowing the lip 68 to separate from the hook 56. This action provides access to void 54 which in turn provides a space for debris to be captured. After FOD event has subsided, the force in the direction of arrow 88 may be overcome by the biasing force of spring 58. If this condition occurs, then the spring 58 may push the lip 68 towards closure by re-engaging the hook 56. This action closes off the void 54 and traps any debris within the voids 54 and/or 82. Various springs 58 having assorted compression characteristics may be employed so as to permit predetermined operational performance.

FIG. 3 illustrates an alternative fan track liner assembly 100 that may be employed with the engine depicted in FIG. 1. The assembly 100 includes an outer surface 102 made of, for example, abradeable material, a core 104, a liner 106, and a spring member 108. A fastener 110 secures the outer surface 102, lip 112 of the liner, and spring or clip 108 together. The clip 108 is c-shaped or hooked-shaped and is nestled within curved wall 50. The clip 108 may be made of metal or other resilient material that is operable to withstand aerospace conditions.

For assembly of the FIG. 3 embodiment, first the aft section 76 is positioned within the cavity 44. The clip 108 may already be installed to the liner 106 so that they are collectively one piece. The nose 114 is then slid into the void 54 and it may snap into position, thus locking the forward portion 66 into place. Fastener 64 may be installed so as to now secure the aft 76 section. The assembly 100 is now secured in place relative to the fan case 36. However, the assembly 100 may be replaced and a new assembly 100 may be installed. Thus, the system disclosed is reparable.

The flexible joint at the aft end 76 of the fan track liner assembly 42 can be a variety of designs, such as an elastic panel piece or a mechanical pin joint, for example. It is designed to allow the assembly 42 to displace as necessary.

FIG. 4 illustrates a graph showing the energies that may be incurred by an aircraft during various operating events. The events are plotted as a function of the deflection of the fan track liner assembly 42 compared to a traditional fan track liner indicating a possible full displacement situation or event. The x axis represents the level of FTL (fan track liner) displacement 120, with units 0-12 depicted showing the scale. A reference point number 10 indicates a point during a full displacement event.

The y axis indicates a level of energy 122 that may be imparted on the assembly 42 due to various events an aircraft may encounter. As the rate of energy increases, so does the potential level of FTL displacement. For example, normal airflow pressure load 124 would be the instance where typical airflow PSI would be encountered given normal aircraft operating conditions. An increase in energy event could next be when a partial fan blade release 126 occurs. A more substantive energy event could be a large foreign object such as ice, debris, etc., 128 impacting the assembly 42. And finally, a high energy event could be a full fan blade release 130. Such an event would be a catastrophic condition where full displacement at level 10 may occur.

As an example, and for illustration purposes only, the energy levels of the following elements are listed below:

-   -   Airflow pressure load=2 energy units     -   Partial fan blade release=4 energy units     -   Large FOD release=6 energy units     -   Full fan blade release=8 energy units         Full displacement of the liner assembly 42 occurs at 10 units on         the displacement scale. The dashed line is intended to         illustrate the performance of the embodiments depicted in FIGS.         2 and 3. The solid line depicts the performance of a traditional         fan track liner assembly. The springed fan track liner         assemblies 42 and 100 begin to displace at an approximate energy         level of 3. By contrast, a traditional FTL may not begin to         displace until an energy level of 7.

The energy level of a released partial fan blade 126 can be lower than large FOD 128. A traditional fan track liner does not displace until some energy more than the large FOD but less than a full released fan blade is applied, at which time it completely displaces through a failure mode. The primary disadvantage of this behavior is that the fan track liner panel will not displace under partial fan blade release energy, thus, not allowing the fan case hook feature to capture that debris. The exemplary embodiments herein can be designed such that they displace sufficiently at energies less than large FOD 128. Here at level 3 the exemplary embodiments begin to displace. The advantage of having full displacement below the energy of a full released fan blade is that the probability of capturing partial released fan blade material is improved and therefore overall system robustness is enhanced. The second disadvantage of a traditional fan track liner behavior is that the range of failure between these two paints can be narrow, promoting a more challenging design space.

The exemplary embodiments are designed such that they do not displace until a predetermined level of energy, more than the normal running condition airflow pressure load, is applied. For example, if the airflow pressure load 124 is at an energy level of 2, then the assembly 42 does not begin to displace until an energy level of at least 3 is achieved. Such arrangement assures the assembly 42 would not displace routinely, causing a loss in aerodynamic performance. The assembly 42 may be designed to perform at certain predetermined events so as to have response characteristics at various energy levels.

The exemplary embodiments could see some partial displacement over a range of energies above the normal running condition airflow pressure load (embodied by the slope of the line). The improved design meets the requirement of tolerating FOD impact but also yielding to released partial fan blade material to allow its capture outside the flow path by exhibiting a novel behavior (for this commodity specifically, not in the general sense) achieved through the introduction of one or more the spring elements.

In operation, the exemplary embodiments offer an advantage in that they are designed to meet various requirements with overlapping energy levels. In particular, they are capable of yielding predictably to an energy that is less than one that it is capable of tolerating without failure.

The design is such that it doesn't matter that both types of debris (external and internal) cause the spring 58 to compress and the core 74 to displace because of the elastic nature of the system. When FOD enters from the front of the engine and strikes the assembly 42, causing the spring 58 to compress and the core 74 to displace, the FOD deflects off of the core and continues into the engine bypass. The spring 58 then expands after the impact and the panel returns to its original position. When fan blade material is released and strikes the panels with forward movement, the spring 58 collapses, the core displaces, and the debris is captured in the fan case hook 56, thus performing its function as required (the severity and infrequency of this kind of event would then drive the engine to be inspected and repaired immediately).

For both the FIGS. 2 and 3 embodiments, the spring member 58 and 108 may be constructed of varying thickness, materials, and may react to various forces that could be generated during a blade off event. It would be helpful to provide a spring member that has a spring biasing value that permits the spring to deform during a blade off event, yet allows the spring member to apply a biasing force downward and maintain the liner assembly in place during normal operating conditions.

It will be appreciated that the aforementioned method and devices may be modified to have some components and steps removed, or may have additional components and steps added, all of which are deemed to be within the spirit of the present disclosure. Even though the present disclosure has been described in detail with reference to specific embodiments, it will be appreciated that the various modifications and changes can be made to these embodiments without departing from the scope of the present disclosure as set forth in the claims. The specification and the drawings are to be regarded as an illustrative thought instead of merely restrictive thought. 

What is claimed is:
 1. A fan track liner assembly for a gas turbine engine comprising: a tray; a panel positioned within the tray; an abradable portion; and a spring element positioned adjacent the tray.
 2. The fan track liner assembly as claimed in claim 1, wherein the assembly is displaceable at energies sufficiently less than energies that are encountered during large foreign object destruction events.
 3. The fan track liner assembly as claimed in claim 1, further comprising at least one fastener for securing the assembly to a fan case.
 4. The fan track liner assembly as claimed in claim 1, wherein the tray has a lip for engaging a hook of a fan case.
 5. The fan track liner assembly as claimed in claim 1, wherein the spring element is a leaf spring, the leaf spring is located near a forward position of the tray.
 6. The fan track liner assembly as claimed in claim 1, wherein the spring element is hook-shaped.
 7. The fan track liner assembly as claimed in claim 6, further comprising a fastening member for securing the spring element to the tray.
 8. The fan track liner assembly as claimed in claim 1, wherein the panel includes a honeycomb core portion.
 9. The fan track liner assembly as claimed in claim 1, wherein the panel has a first thickness, and a second thickness, the first thickness is biased by the spring element, the second thickness is positioned adjacent an inside surface of a fan case.
 10. The fan track liner assembly as claimed in claim 1, further comprising a fan case, the fan case having a cavity and a fan hook.
 11. A fan track liner assembly for use with a fan containment case for a gas turbine engine comprising: a fan track body having a first surface, an inner core and a second surface, the first surface is made of abradable material and is operable to engage a blade member, the inner core is made of collapsible material that is operable to be deformed during a catastrophic condition, the second surface has a profile that is configured to substantially mate with an inside surface of a fan case; a first mounting member for attaching the fan track body to a fan case; and a spring positioned between the fan track body and a fan case.
 12. The fan track liner assembly as claimed in claim 11, further comprising a fan case for a gas turbine engine.
 13. The fan track liner assembly as claimed in claim 11, wherein the fan track body can move from a static position to a partial fan blade release position, and then revert back to a static position, without deforming the inner core.
 14. The fan track liner assembly as claimed in claim 11, wherein the second surface of the fan track body is a liner.
 15. The fan track liner assembly as claimed in claim 11, further comprising a void between the second surface of the fan track body and a surface of a fan case for a gas turbine engine.
 16. The fan track liner assembly as claimed in claim 11, wherein the inner core is a sandwiched between the first surface and the second surface, the inner core comprising: a honeycomb core having pockets of open space, and epoxy located within the pockets of open space.
 17. A fan track liner assembly for use with a fan containment case for a gas turbine engine comprising: a fan containment case for a gas turbine engine, the fan containment case including a fan case hook, a cavity, and a mounting member; a fan track liner having an external profile that is configured to fit substantially within the cavity of the fan containment case; a void positioned between the fan containment case and the fan track liner; and a biasing member positioned within the void.
 18. The fan track liner assembly as claimed in claim 17, wherein the fan track liner includes an abradable material which is positioned to engage a blade member.
 19. The fan track liner assembly as claimed in claim 17, wherein the fan track liner includes a core comprised of deformable material.
 20. The fan track liner assembly as claimed in claim 17, wherein the biasing member is connected to one of the fan containment case or the fan track liner, the biasing member is positioned near a forward portion of the fan track liner. 